Method of and apparatus for bluing porcelain



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Feb, 19 1924 I c. DRESSLER METHOD OF AND APPARATUS FOR BLUINGIEORCELAIN Original Filed May 17 2 amoe htoz 6 Q 9 1 I I.

7 .tion'.

Patented Feb. 19, 1924.

UNITED STATES P'ATENT OFFICE.

CONRAD DBESSLER, OF CLEVELAND, OHIO, ASSIGNOR TO AMERICAN DRESSLER TUN- NEIJ KILNS, Inc, or NEW YORK,

N. Y., A CORPORATION OF'NEW YORK..

METHOD OF AND APPARATUS FOR BLUING PORCELAIN.

Application filed May 17, 1920, Serial No, 3'82,(:,04. Renewed July 17, 1923.

To all whom it may concern:

Be it known that I, CONRAD Dnnssnnn, a subject of the King of Great Britain, and resident of Cleveland, in the county of C-uyahoga and State of Ohio, have invented certain new and useful Improvements in Methods of and Apparatus for Bluing Porcelain, of which the following is a specifica The general object of the present invention is to provide for the efficient bluing of porcelain in a continuous tunnel kiln.

In bluing porcelain it is ne cessary,in order to effect certain desired'chemical reactionsand physical changes in the porcelain, to subject the latter to different atmospheres in different stages of the firing operation. In the ordinary process of bluing porcelain in an intermittent kiln, the porcelain packed in wadded saggers, is subjected in an initial stage of the firing operation to a reducing atmosphere, mainly, I believe, because it' is practically difficult to have any other kind of an atmosphere in the kiln when the fire in the latter is being started. After a short initial period, the atmosphere in the kiln is given an oxidizing character by supplying air at a rate fuel being burned, and this oxidizing atmosphere is 'maintained throughout the major portion of the heating up stage, partly because it isnecessary to get rid of the smoke which has penetrated the saggers in'the initial firing with a reducingatmosphere, and

partly because all carbonaceous matter must be burned out of the porcelain in order to produce a product which is white to the core. When the porcelain approaches its final temperature and before th felspathic glaze commences to vitrify, a reducin atmosphere is maintained in the kiln short period in order to reduce the small amount of iron at the-surface of the ware.

from red iron oxide to the black ferrous-ferric oxide and thereby give the porcelain the desired bluish tinge. Finally the ware is subjected'again to an oxidizing temperature at the stage n which the glaze begins to flow. This final oxidizing stage is desirablegreater than that required for the complete combustion of the ed type known Dressler type in which the kiln ora.

cuts in the glaze which should exist in the finished ware in the form of metallic oxides and not in the metallic form. In the actual practice of bluing porcelain in an intermittent kiln, it is common to divide the reducinto two reducingperiods with an intervening oxidizingperlod. This sub-division is due mainly or wholly, I believe, to the diflipart the reducing effect in two small impulses with an intervening oxidizing effect than by a single strong reducing impulse. One object of the present invention is to provide for the subjection of the ware as it passes gradually through a continuous tunnel kiln to conditions closely approximating those which have'been found to ive satisfactory results when the ware is red in an intermittent kiln. I believe, however, that with the better control of the kiln atmos- 'phere and temperaturesattainable with the present invention, and 1n "view of the, fact that with it, it is unnecessary to pack the porcelain in tightly closed saggars, a single reducing atmosphere stage intervening between the primary and secondary oxidizing atmosphere stages will be sufficient. With m'ypresent invention I regard it as wholly unnecessary to employ the initial reducing atmosphere stage.

In carrying out my invention I employ a continuous tunnel kiln of the muffle heatand preferably a kiln of the well chamber is heated by internal combustion chambers and the transfer of heat from the internal combustion chamber to the ware is primarily by means of convection currents ing stage preceding the final oxidizing stage of the kiln atmosphere. With a kiln of this j character it is comparatively simple to maintain a very precise control of the temperature conditions in different zones or sections of the kiln chamber, and it is also readily possible, with the special provisions hereinafter illustrated and described to mantain determined atmospheres definite in character and differing from'one another in successive zones or sections of the kiln chamberL The various features of novelty which illl characterize my invention are pointed out 1 but on a larger scale and showing only a portion of the kiln shown in Fig. 1.

Fig. 3 is a transverse section taken on the line 3-3 of Fig. 2; and

F i 4 is a partial sectional plan taken on the-hneea of Fig. 3.

In the drawing A represents the horizontally elongated kiln chamber of a continuous tunnel kiln, which is shown as formed withbenches at opposite sides of the pathway through the kiln for the goods carrying cars J. These cars enter the kiln at one end past a normally closed entrance door A and leave it at the opposite end past a normally closed exit door A vVith the type of kiln illustrated, the porcelain ware carried through the kiln on the cared, maybe exposed to the kiln atmosphere, and is enclosed in saggars only when these form con venient means for iving the easily deformed ware its desired supports, and'in such cases, the saggars need not be wadded to prevent free contact between the ware and the kiln atmosphere. 0n each of the benches A, for an intermediate portion of the length of the kiln chamber, is located a combustion chamber B. Each combustion chamber B as shown is connected at one-end.

to a group of tubes C which run to the entrance end of the kiln where they connect with a header C. The headers C are con nected, as by a tunnel C to a suitable stack or: exhaust fan, not shown, for creating the (necessary 'draft to draw the products of combustion out of the combustion chambers and through the pipes C which form exten-- sions of the combustion chambers. Between the opposite end. of each combustion chamber and the exit end of the kiln chamber, a

group of tubes D is located on the: corresponding bench A. These receive cold air as through the port D at the exit end of the kiln, and deliver it much hotter into a c0rresponding header D shown as connected to a duct D which is connected in turn to the inlet of a fan E. The latter has its outlet connected, as shown, to a conduit EjA= through which a portion of the air passing through the fan is delivered to one or more burners in each combustion chamber adja cent the end thereof most remote from the meagre stack connection. Air passing the fan E in excess of the burner requirements may be passed -to a drier or otherwise disposed of througha branch pipe EA. Gas for combustion in the combustion chambers is supplied through suitable connections which may be branches or the gas conduits I hereinaiter referred to. 3 Each combustion chamher has its walls formed for the most part of tile sections 5 which extend transversely to the length of the combustion chamber and in the bottom wall sections, and are connect ed at their upper ends to the channels 5' in the tile sections forming'the top wall of the combustion chamber. The tile sections forming the topwall of the combustion chamber are inclined, as shown,.and the upper ends of the channels I) thereinare open to the kiln chamberas may also, though not necessarily, be the case with th lower ends of these. channels. With the combustion chamber construction described",.a gravity circulation of the kiln atmosphere is produced by currents of the kiln atmosphere which enter the channels 6' in the bottom walls of theycombustion chambers,jrise and are heated as they rise, through the channels 7) in the side; walls of the combustion chambers, and pass out into the ki'n chamber structure at the top of the latter through 4 the chanen ls b in the top wall portions; of the combustion chambers.- These currents descendthrough the goods pathway, and 'in descending impart a portion of their heat to I the goods. in so far as above described the kiln illustrated is a typical Dressler kiln having combustion chambers ofthe general character disclosed in my prior Patent The kiln shown differs from ordinary- 'Dressler kiln in' that an intermediate portion of the kiln chamber including the kiln zone of highest temperature, and an ad.- jacent portion oat-the kiln at the entrance end.

side of the high teinperaturezone is divided into a series of cainpartments a, "a, a; a,

a, a aa and a by transverse partition walls Wlnch include special combustion chamber section's B, barriers lB mounted thereon, andtransverse partition walls F depending-from the roof of the kiln. These compartments communicate with one. another through the central openings in the partition walls between them .formed for the passage of the goods on the cars J. These openings are preferably restricted so as to give the smallest clearance possible consist G. As shown there are two of these outlets ceive steam the spaces in the various compartments lying above the lower edges of the depending partitions F. Each of the compartments a, a, a is provided with one or more outlets for each compartment. These outlets each comprise av stack rising from the top of the kiln and provided with its own regulating damper G, Advaritageously one or more outlets G may be provided for the kiln portions immediately adjacent the opposite ends of the series 'of compartments a, a, and (1 Associated with each of the compartments a, a", and 0 are means for injecting a gaseous fuel into the compartment to modify and control the atmosphere therein. The preferred means shown for this purpose comprises a series of inlet passages A formed through the side walls of the kiln chamber and parallel in; direction and located at the same level as the channels I) in the bottom walls of the; combustion chambers. Nozzles H enter the outer ends of the passa es A and the outer endof each .nozzle may receive gas from a gas supply pipe I through a corresponding valved con nection I, may receive air from a compressed air supply pipe J through a corresponding valved connection J and may refrom; a steam supply pipe K through a correspondingI valved connection K extends into the K. As shown the pi e and is arranged so body of the nozzle that the jet of air or steam discharged may act as anejector jet for drawing gas from the corresponding connection I and passing it with the desired velocity into the kiln through the corresponding nozzle H.

In the preferred mode of operation contemplated, an oxidizing atmosphere is maintained in the compartments a and a and a reducing atmosphere is maintained in the compartments a. The oxidizing atmospheres are maintained in the compartments 0 and .a by the,injection of air into these kiln chambers through the corresponding nozzles H from the air supply ipe K. Preferably this air is highly pre eated and it may advantageously be supplied by the blower E with air heating means interposed between the blower and the nozzles H, though no air heating means of this character are shown. The reducing atmosphere in the compartment a may be maintained by supplying gas only to this compartment through the corresponding nozzles H, but some air may advantageously be mixed with the combustible gas supplied by the nozzles H. The air thus supplied should be insuflicient, how- 'ever, for the complete combustion of the gas which would destroy its reducing character. The partial combustion of the gas imparts some heat to the kiln chamber compartments a which is sometimes desirable. In lieu of using air to prevent carbon deposits, steam,

or a mixture of air and steam. may be supplied. The use of steam in conjunction with the combustible gas is desirable, in that it effectually prevents carbon deposits in the channels b and the resultant mixture of hydrocarbons, carbon monoxide and hydrogen resulting from the interaction of the.

steam and gas is highly reducing. The interaction between the steam and gas is endo- 'thermic and thus tends to lower the temperature in thecompartment-s a, but the amount of gas and steam which it is necessary to pass into the compa'rtments a in order to maintain a strongly reducing atmosphere therein, is comparatively small and the heat loss from the endothermic reaction is relatively insignificant. It is to be noted moreover that with the comparatively small flow of air or gas'or steam or mixtures thereof required for the maintenance of the desired atmospheres, the fluids flowing through the channels b can be heated in their passage through the latter, so that they issue from .the latter into the kiln chamber proper at the same general temperature as the kiln atmosphere into which they are discharged.

With the construction described it is readily possible to maintainan oxidizing atmosphere, a reducing atmosphere, or if need be a neutral atmosphere in any one of the compartments a, a -and a. All that isrequired is to introduce the proper gaseous constituents into the compartment through the corresponding nozzles H. This ready control of the character of the atmosphere in the various compartments a, a and a makes it possible to shift the various oxidizing and reducing atmosphere zones longitudinally of the kiln chamber, if and when this may be desirable to et. the best operating results for any particular purpose and with any particular conditions in the kiln. The structure also permits the maintenance of other arrangements of oxidizing and reducing atmosphere zones than the preferred contemplated arrangement specified above. By properly. regulating the rate at which gas= eous substances are admitted to the kiln chamber through the nozzles H and the suction through the various stack outlets G, it is ossible to avoid appreciable flow longitudinally of the kilnfrom one compartment into another without creating pressure or flow conditions inthe various compartments 0., a and a preventingsuch circulation of the atmosphere thereln, as is deriers or bafies empldyefd" to facilitate the maintenance of separate'kiln atmospheresin adjacent compartments isnot. specifically claimed herein asit is so claimed in my 00-- pending application, Serial No, 382,001 filed concurrently herewith.

in the construction illustrated, see particularly Fig. 4, the spacingof the nozzles H is not the same as that of the channels I) in the bottom wall of the combustion chamber. The purpose of this is to insure an appreciable flow through each of the channels Z2 adjacent the nozzles H notwithstanding :the bodily movement of the, combustion chambers B lengthwise on the sup- 7 porting benches whiclnoccurs in practice on the thermal expansion and contraction of the apparatus, such relative movement of the combustion chambers and kiln walls prevents the maintenance of exact registry of the nozzles H and channels I).

lVhile in accordance with the provisions of the statutes Ihave illustrated and de- LII ' muifie heating means therefoig of means for scribed the best construction for, and mode of carrying out my invention now known to me, it will be apparent to those skilled.

injecting fluid into a localized portion of the kiln chamber to make the atmosphere in that portion of the chamber either oxidizingor reducing as'desired. v

2. The method of glazing porcelain which consists in passing the ware to be-gIazed through an elongated kiln chamber heated to which the reducing first gradually raise the wars to a predetermined temperature and then eool'the ware as it passes through the chamber, and maintaining a reducing atmosphere in an inter mediate portion otthe kiln chamber and exidizing' atmospheres in portions of the kiln chamber. atthe opposite sides or said intermediate portion. a

3. In a tunnel kiln thecombination with the kiln chamber, of'a combustion chamber therein having a bottom wall formed with open ended horizontal channels extending transversely to the kiln chamber and having upper walls formed with channels extending transversely to the combustion chamber and ommunicating at their lower ends with said bottomwall channel and open at their upper ends to the kiln chamber and nozzles mount ed in the side wall of the kiln chamber for discharging fluid into the interior of the kiln chamber through the bottom wall channels of the combustion chamber to/thereby control the atmosphere in an adjacent portion of the kiln chamber.

4. In apparatus for treating porcelain-the combination of a continuous tunnel kiln comprising an elongated kiln chamber, mufiie heating meansytherefor, baffles within the kilnchamber providing a series of compartments therein connected by restricted openings normally obstructed to a substantial degree by the goods passing through said openings, means for injecting gaseous substances into the different compartments and for withdrawing gaseous substances therefrom to thereby maintain, a reducing atmosphere in one or more of said compartments and an oxidizing atmosphere in one or more adjacent compartments at each side of the compartment or compartments in atmosphere is vmaintained.

.Signed at Cleveland, in the county of Cuyahoga and State of Ohio, this 12th day.

of May, A. D., 1920.

CONRAD DRESSLER. 

